During the drilling and completion of wellbores, objects such as drill pipe, collars, downhole tools and other apparatus sometimes becomes stuck due to differential sticking, key seating, hole sloughing and other conditions. In such situations the stuck object sometimes cannot be freed by application of ordinary tensile or compressive forces from the surface, but may be freed by downhole delivery of sharp jarring forces.
Apparatus for delivering jarring forces ar typically known as jars. Jars generally include an outer housing which is attached to the stuck object, and, a tubular member telescopically connected therein which is attached to pipe, coiled tubing or wire from the surface. Typically contained within the jar is a force responsive latch means, which maintains the jar in a "set" position until a preselected axial force is exceeded, at which point the latch mechanism"releases", allowing the jar to "stroke" and deliver a jarring impact to the stuck object. Examples of such jars are shown in Buck U.S. Pat. No. 4,889,198; De Cuir U.S. Pat. No. 4,865,125; Buck U.S. Pat. No. 4,688,649; Clark U.S. Pat. No. 4,376,468; Taylor U.S. Pat. No. 4,333,542. Such jars may be utilized alone, or in cooperation with downhole means to store, or accumulate, an increased amount of energy to be delivered to the stuck object.
Downhole apparatus for accumulating an increased amount of energy to be released as a jarring impact are typically referred to as accelerators, but are variously referred to as jar boosters, accumulators or intensifiers. The primary function of such devices, which are typically inserted into the work string near the jars, is to store an increased amount of energy in response to upward or downward displacement of the work string, for enhancement of the jarring impact on the stuck object when the jar strokes. Examples of such devices are shown in Anderson, et al U.S. Pat. No. 4,846,273 and Taylor U.S. Pat. No. 4,844,157.
Not previously known is a combined accelerator and jar mechanism within an integral outer housing, which utilizes the mass entire outer housing as a movable hammer. Also not previously known is a combined accelerator and jar, within an integral housing, which is capable of imparting both "up" and/or "down" impacts, in any desired number and/or sequence of impacts, in either direction. Also not previously known is a jar utilizing rigid latch bars which, through tapered shoulders, cooperate with a spring biasing means whose compression may be adjusted, so as to allow selection of the amount of jarring impact delivered to the stuck object.